This callback is similar to pdfSetMouseUpCbk, except that (a) it
is called with window coordinates instead of PDF coordinates, and (b)
it will be called even if the mouse is clicked outside of a PDF page.

IMPORTANT: In order to receive pdfSetMouseMoveWinCbk and
pdfSetMouseUpWinCbk callbacks when the mouse is outside
the XpdfViewer window (not just outside the PDF pages), you must
call SetCapture in the pdfSetMouseDownWinCbk
callback. See the example below.